The focus of this work is the early childhood etiology of problem aggression. Groups of problem-aggressive and control children at several different ages are compared in terms of the following questions: (1) How do children behave in aggressive and nonaggressive interactions with family members and peers? (2) Are there distinctive ways in which others act towards aggressive and nonaggressive children? (3) What explanations do children provide for their own, and others', aggressive behavior? There are two primary sources of data. The first is mothers' observations, reported in narrative, of aggressive incidents involving the child during the daily course of events in the home. The second source of data is investigators' reports during home visits of the general interactions of children with family members and peers.